NY Times Article: Breast Feeding Linked to Lower Cancer Risk

There is new evidence that breast-feeding is associated with a lower incidence of breast cancer among a group of younger women who are at particularly high risk: those with breast cancer in the family.

Although several studies have found that lactation is protective against breast cancer, the new report found little effect for premenopausal women over all. But for women with an immediate relative, like a mother or a sister, who had breast cancer, those who breast-fed had a 59 percent lower risk of premenopausal breast cancer. That is closer in line with the risk for women who had no disease in the family, the study found.

“I was sort of stunned,” said Dr. Alison M. Stuebe, the first author of the study and an assistant professor of obstetrics and gynecology at the University of North Carolina, Chapel Hill. “It’s an impressive reduction in risk. Other studies either hadn’t looked at this or didn’t include enough women with a family history to find a statistically significant difference.”

The new study, published in The Archives of Internal Medicine, used information from 60,075 participants in the second Harvard Nurses’ Health Study. More research is needed to replicate the findings and to show that the reduced risk is the result of breast-feeding, rather than some other factor common to women who breast-feed. But Dr. Stuebe suggested that breast-feeding may prove just as effective a strategy for high-risk women as the use of Tamoxifen, a drug that interferes with estrogen activity and is often used in high-risk women to reduce breast cancer risk.

Though breast-feeding is promoted primarily because it is linked to better health in babies, mothers seem to accrue long-term advantages. Studies have found that women who breast-fed are less likely to develop osteoporosis and ovarian cancer, as well as high blood pressure and heart disease decades later.

Because women who breast-feed tend to be more educated and to have higher incomes than those who bottle-feed, disentangling the effects of lactation from those of other habits and behaviors can be difficult.

In the latest study, the data came from women who participated in the Nurses’ Health Study from 1997 to 2005. The women had all given birth and provided detailed information about their habits and medical history, including breast-feeding, in 1997, before any had developed breast cancer. About 87 percent of the women had breast-fed for at least some period. By June 2005, premenopausal breast cancer had been diagnosed in 608 women. The women who had breast cancer in their immediate family but who had breast-fed had developed only 41 percent as many cancers as those who had an affected relative but refrained from breast-feeding.

But there was no greater benefit if women breast-fed exclusively or for longer periods of time, raising questions about the study’s conclusions, said Dr. Louise Brinton, chief of the National Cancer Institute’s hormonal and reproductive epidemiology branch.

“I would be cautious in interpreting this,” Dr. Brinton said. “You would expect to see a dose-response relationship with breast-feeding if it is a really causal protective factor.”

Interestingly, women who took drugs to prevent the formation of milk were at lower risk for breast cancer than those who refrained from breast-feeding but did not use lactation-suppressing drugs, the study found.